1. Field of the Invention
The present invention relates to peripheral data processing subsystems and particularly those subsystems employing electrical and logical connections between a controller and a plurality of peripheral devices. The peripheral devices are preferably data storage devices.
2. Discussion of the Prior Art
Information-bearing signal recorders employing disks with spiral tracks have been used for years for recording video signals and composite (video, audio and control) signals. The usual mode of operation used in such disk recorders causes a transducer means to continuously follow a spiral track on a disk for presenting video as a series of frames to create a reproduced motion picture. Each circumvolution, or turn, of the spiral track usually stores two picture frames or one video image (two video frames are interlaced to create one image). Still framing, also termed "stop motion", is achieved by interrupting the spiral scanning by causing the scanning transducer means to either repeatedly scan the same circumvolution of the spiral or store the video signals read from one circumvolution in a signal buffer separate from the video disk player. For example, the Oprandis et al. patent U.S. Pat. No. 4,338,629 shows a specific stop-motion control causing the transducer means to jump from one circumvolution to the immediately preceding circumvolution for each rotation of the video disk. U.S. Pat. No. 4,332,022 shows another stop-motion control for video disk players.
While the usual video presentation requires a continuous scan of successive circumvolutions in the spiral track to recreate the video, using stop-motion controls without "tearing" the picture apparently requires either special controls or buffering of the video-bearing signal. An example of one control to avoid picture tearing is shown in Prasad et al. patent U.S. Pat. No. 4,396,961.
The format of signals in a spiral track can be crucial to successful operation of a disk recorder employing such disk media. The Mes patent U.S. Pat. No. 3,931,457 shows a video disk format having a nonvideo angular sector for each circumvolution with all of the nonvideo sectors lying along a common radial line. One portion of the nonvideo sector, a norecording area, is a starting or orienting area, while another portion of the nonvideo sector stores the address of a corresponding circumvolution. Frame synchronization signals are also provided. The nonvideo sector apparently corresponds to "flyback" time of a display used to display the carried image. This patent also teaches that either plural concentric tracks or a single spiral track may be employed. The spiral track is illustrated.
While a single spiral track on a disk has been employed for video disks which store one image per turn or circumvolution of the spiral track, data recorders, particularly ones employing magnetic disks, have almost always used concentric tracks for facilitating random access to the stored data. The record surface of the disk is divided into equal angular-sized data-storing sectors, each sector usually having track- and sector-identifying data in addition to storing data. Many of the data-storing disk recorders employ a stack of coaxial co-rotating disks which are simultaneously scanned respectively by a plurality of heads mounted on a common support radially movable with respect to the disk. In this manner, one track on each of the co-axial disks can be accessed without radially moving the common support. Generally, access to the various simultaneously-scanned tracks is serial, with electronic circuits switching and controlling which track is to be accessed. All tracks having a common radius are termed a "cylinder of tracks".
In this arrangement, occasions arise wherein the data contents of more than one track in a cylinder are to be transferred as one unit of data. To avoid rotational latency delays inherent in disk recorders, a so-called roll mode is employed, such as described in the IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 13, No. 1 in an article by D. A. Stevenson "Transparent Roll Mode for Rotating Device" on pages 93-95 (June 1970). In the roll mode, access to a first track in the cylinder occurs at the first-encountered sector to be transferred, then the data to the end of that track and of all other tracks is transferred, followed by transferring the data on the first track that was not initially transferred. This arrangement employs electronic switching to make the series of concentric tracks appear as a single track which can be conceptually viewed as a helix. An implementation of the roll mode is also described in the IBM Newsletter No. GN26-0351, Nov. 15, 1979, on pages 79 and 80.
In any disk data recorder, it is desired to simplify the controls yet provide efficient operation. Optical video recorders offer a high areal density of recording greater than that of the present-day magnetic disk data recorders. It is desired to take advantage of such areal density. To quickly do so, it is advantageous to employ the track layout usually found in video recorders, i.e., the single spiral track rather than the random-access-oriented concentric tracks. Therefore, a simple but effective control is desired for using the video spiral track disks for data recording which emphasizes random access as desired for use in data processing systems.
Another important aspect of data-storing disk recorders is the electrical and logical connections and control electronics which enable access to data-storing sectors of a data storage disk. Since costs are an ever dominant factor in manufacturing such disk recorders, the connections and associated control electronics should be simple, yet allow a maximal flexibility for growth in data capacities while enabling efficient access. Connections of peripheral devices to host processors and control units/controllers have employed so-called tag control lines which are operationally associated with data transfer lines or buses. The Moyer et al. patent U.S. Pat. No. 3,303,476 also shows using such tag control lines for setup and termination of peripheral data transfers. The address of the peripheral device which will participate in such transfers is sent over the data lines to the peripheral devices. Moyer et al. show a so-called "daisy-chain" connection wherein all peripheral devices in the daisy chain are connected to one subchannel of a host processor. In the Moyer et al. system, like the peripheral connections of the International Business Machines Corporation (IBM) host processors, data is transferred over one-way data buses termed Bus Out and Bus In. The IBM peripheral connecting system is described in the IBM publication GA22-6974-4 "IBM System/360 and System/370 I/O Interface Channel to Control Unit Original Equipment Manufacturers' Information" on pages 7 et seq. (dated 1978). All operations, control and data transfers conducted between the host processor and any peripheral device require that the peripheral device be "selected". "Selected" is a term that means that one and only one of the peripheral devices on any one daisy-chain connection can be active with the host processor at a given instant of time. This restriction does not prevent daisy-chain-connected peripheral devices from performing so-called "free-standing" operations during the same instant of time, i.e., operations that do not require host supervision. Examples of such free-standing operations are rewinding tape in tape recorders, seeking tracks in disk recorders, performing diagnostic functions, and the like.
Levy et al. patent U.S. Pat. No. 3,999,163 shows peripheral-device-to-control-unit connections termed "synchronous" and "asynchronous" which correspond largely to the data buses and tag lines of Moyer et al., supra. Still, no action occurs between the peripheral device and the control unit without a device selection which identifies a peripheral operation with one, and only one, peripheral device.
The U.S. patent to Bauer et al. U.S. Pat. No. 4,423,480 shows control-unit-to-peripheral-device connections having three portions, a first portion for transferring data, a second portion consisting of tag control lines which includes a device selection line (Select Out) which enables the usage of the data lines (first portion) and the other tag control lines in the second portion. A third portion of each such connection transfers commands from the control unit to any addressed peripheral device on the same daisy-chain connection independently of the selection for enabling preparatory actions by the various peripheral devices independently of device selection. This arrangement allows overlapping the peripheral data transfers with preparatory actions (tape motions, etc.) without requiring the preparing addressed peripheral device to be selected for a peripheral operation. A significance of this arrangement is that the preparatory actions can be initiated with one device while another device is selected for transferring data with a controller or host processor.
In spite of all of the advances and flexible connections and controls mentioned above, a need still exists for yet a simpler and lower-cost device connection, including a small number of electrical lines extending between the controlled and controlling units and that still provides flexible device controls. Such simplicity and low cost are important to success of peripheral subsystems which attach to low-cost host processors, including the so-called personal computers.